4-Methyl-7,10-dihydrobenzo[h]coumarin (4) was prepared by condensation of ethyl acetoacetate with 5,8-dihydro-l-naphthol (7), which was obtained by Birch reduction of 1-naphthol (6) . It was found that the reaction conditions, particularly the presence of acid and the absence of oxygen, were critical for the condensation reaction. Under the acid-free condition, 3-acetyl-2-hydroxy-6-methyl-pyran-4- one (8) was obtained and its structure was confirmed by X-ray diffraction analysis. In the presence of acid, the condensation of 7 with ethyl acetoacetate proceeded to give a mixture of the expected product 4 and an aromatized derivative 4-methyl-benzo[ h]coumarin (5) . Under the optimized conditions (under Ar atmophere with CH_3SO_3H as catalyst in the presence of antioxidant Na_2S0_3), 4 and 5 could be obtained in 49.1% yield with chemical selectivity of 70 = 30 (4:5)

Key words: COUMARIN, PYRANE P, NAPHTHALENOL P, XRD, SODIUM SULFITE, ANTIOXIDANTS